Application of Laser-enhanced Ionization Spectroscopy: Effect of Dissociation Constant on the Atomization Efficiency Determination in an Acetylene-Air Flame

摘要

By using laser-enhanced ionization (LEI) technique, we have studied atomization efficiencies of the alkali halides in an acetylene/air flame. As an aqueous soltion of the metal salt was nebuilized into the burner head, a flame with a high temperature of about 2500 K may cause dissociation of the ionic bond to release the free metal atoms. The ratio of the number density of free metal atoms present in the flame to the total number density of the same metal element nebuilized determines the atomization efficiency. In this work, binary salt solutions including LiX, NaX, and KX (X = Cl, Br, and I) were used; each was prepared at 5 ppm (#mu#g/mL) metal concentration. The atomizatin efficiency of the metal element was measured, as the accompanied halogen species was varied. We found that the ratios of atomization efficiencies of the alkai element in different halide compounds were almost equal to one. Atomization efficiency determination is dominated by the metal atom, but weakly influenced by the binding halogen species. The observation may be interpreted satisfactorily by using the Sugden-Bulewicz model. Based on this model, the metal atomization efficiency for different halide compouinds depends on the number densities of the halogen atoms and the related dissociation constants.For the binary salt with a small concentration and a large dissociation constant, the atomization efficiency determination tends to be dominated by the metal atom alone.